The present disclosure relates to a method for protecting a diesel particulate filter (DPF) in the exhaust section of an internal combustion engine of a motor vehicle from unintentional combustion of soot in the DPF and high temperatures with the DPF and to a motor vehicle set up to carry out the method.
A wall flow DPF in the exhaust section of the internal combustion engine of a vehicle stores solids contained in the exhaust gas, in particular soot, primarily on the wall of the DPF. The solids which have accumulated on the internal wall of the DPF increase flow resistance and hence exhaust gas backpressure, reducing engine power and increasing fuel consumption. In order to return the exhaust gas backpressure to its desired value, the DPF may be regenerated upon accumulation of a pre-determined mass of soot build-up within the DPF. Regeneration can be done passively through the engines exhaust heat or may be initiated intentionally by a control system.
In the case of a DPF which is heavily laden with soot, the exothermal heat generated in regeneration may raise the temperature of the DPF to a point that may compromise its structural of chemical integrity leading to degradation of the DPF system. This degradation to the DPF can be lessened by monitoring the temperature of the exhaust gas emerging from the filter, for example, and reducing the oxygen concentration in the exhaust gas entering the DPF to very low levels if combustion of soot in the DPF occurs unintentionally or at temperature above a determined degradation threshold is detected, thus reducing the exothermal reaction resulting from the combustion of soot. Lowering the oxygen concentration of exhaust gas can be achieved by operating in stable stoichiometric combustion conditions wherein substantially all (e.g., more than 98% of) fuel is combusted, which leads to sustained low oxygen concentrations in the engine exhaust gas and hence to a reduction in the soot combustion rate in the DPF. As an alternative, the exhaust gas mass flow through the DPF may be set to zero by switching off the internal combustion engine completely. However, in the case of lean burn engines such as diesel engines, it is not possible to operate the internal combustion engine a stoichiometric conditions over a wide range of engine operating states.
The inventors recognized the above interrelated issues, and that these operating constraints may be advantageously addressed in hybrid vehicles by initiating a DPF protection mode when exhaust temperature from the DPF exceed a threshold by decoupling the combustion engine from the wheel drive train during regeneration such that the vehicle is propelled solely by the electric motor, and the engine speed and/or load can be set to a range enabling stable combustion at stoichiometry. Further, by coupling the engine to an alternator generating power for a motor battery, fuel loss can be mitigated and battery charge preserved.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.